As shown in the attachments of this post,
there is no superimposed pressure.
All load are nodal loads in FEM, so your first comment doesn't apply to this case.
Secondly, I tried to optimize the problem with top and bottom facesheets
linked together in the first place as found in the second attachment,
only to witness the weight becomes even greater.
That's because the thickness of top facesheet follows that of bottom facesheet,
while bottom sheet has to be thick but top sheet doesn't need to be so, though.
This means I think that load distribution to each part doesn't change
regardless of whether two sheets are linked or not.
What do you think of this...?